Characterization of Salmonella Phage P1-CTX and the Potential Mechanism Underlying the Acquisition of the blaCTX-M-27 Gene

Abstract

The P1 phage has garnered attention as a carrier of antibiotic resistance genes (ARGs) in Enterobacteriaceae. However, the transferability of ARGs by P1-like phages carrying ARGs, in addition to the mechanism underlying ARG acquisition, remain largely unknown. In this study, we elucidated the biological characteristics, the induction and transmission abilities, and the acquisition mechanism of the bla_CTX-M-27 gene in the P1 phage. The P1-CTX phage exhibited distinct lytic plaques and possessed a complete head and tail structure. Additionally, the P1-CTX phage was induced successfully under various conditions, including UV exposure, heat treatment at 42 °C, and subinhibitory concentrations (sub-MICs) of antibiotics. Moreover, the P1-CTX phage could mobilize the bla_CTX-M-27 gene into three strains of Escherichia coli (E. coli) and the following seven different serotypes of Salmonella: Rissen, Derby, Kentucky, Typhimurium, Cerro, Senftenberg, and Muenster. The mechanism underlying ARG acquisition by the P1-CTX phage involved Tn1721 transposition-mediated movement of bla_CTX-M-27 into the ref and mat genes within its genome. To our knowledge, this is the first report documenting the dynamic processes of ARG acquisition by a phage. Furthermore, this study enriches the research on the mechanism underlying the phage acquisition of drug resistance genes and provides a basis for determining the risk of drug resistance during phage transmission.

Keywords: P1-CTX phage; Salmonella; acquisition mechanism; blaCTX-M-27.

Figure 1

P1-CTX phage activity. (A): P1-CTX phage plaque; (B): transmission electron microscopy image of P1-CTX phage; (C): induction efficiency under different conditions. MitC: mitomycin C; CIP: ciprofloxacin; GEN: gentamicin; AMI: amikacin; KAN: kanamycin; CL: colistin; MER: meropenem; SUL-TMD: sulfamethoxazole-trimethoprim; CHL: chloramphenicol; FOS: fosfomycin; CTX: cefotaxime; UV: ultraviolet.

Figure 2

Target site analyses of Tn1721-bla_CTX-M-27 transposons. (A): Sequence comparison of P1-CTX phage and P1 phage in HYM1 and T-HYM1; (B): transposition diagram of transposon Tn1721-bla_CTX-M-27 between P1 phages; (C): target site analyses of Tn1721 transposons.